WEDNESDAY, July 3 (HealthDay News) -- For people who suffer a spinal cord injury, irreversible tissue loss occurs within 40 days, which is much sooner than previously thought, researchers say.

The investigators used new MRI techniques to assess 13 people with spinal cord injuries. The patients were checked every three months for a year after their injury. After 12 months, the diameter of the spinal cord was 7 percent smaller.

Lesser declines were also evident in the corticospinal tract (which is critical for motor control), and nerve cells in the brain's sensorimotor cortex (which integrates the senses and the motor system), according to the researchers at the University of Zurich in Switzerland and University College London in the United Kingdom.

"Patients with a greater tissue loss above the injury site recovered less effectively than those with less changes," researcher Patrick Freund, of the University of Zurich, said in a university news release.

The study was published July 2 in The Lancet Neurology.

Until now, it had been believed that it took years before tissue changes in the spinal cord and brain above the injury site could be detected. This study shows that tissue loss occurs much earlier and that newer MRI technology can identify these tissue changes and be used to assess the effects of treatment, the researchers noted.